Water-insoluble carboxyl-containing polymers are generally obtained by copolymerizing a carboxyl-containing unsaturated monomer and other unsaturated monomer(s) by emulsion polymerization, suspension polymerization or solution polymerization using an organic solvent. In the case of emulsion polymerization or suspension polymerization, it is difficult to obtain a copolymer having a uniform composition because the carboxyl-containing unsaturated monomer dissolves in water. It is therefore effective for obtaining a copolymer having a uniform composition to conduct solution polymerization using an organic solvent in which both an unsaturated monomer and the polymer produced dissolve uniformly.
Processes for recovering the water-insoluble polymer as produced by solution polymerization in a powdered form include a process comprising removing the organic solvent by evaporation to dryness and grinding the residual solid polymer and a process comprising adding a poor solvent for the polymer, such as water, to the organic solvent solution of the polymer to precipitate the polymer.
The former process is inefficient because great energy is required for removal of the solvent and unreacted monomers. On the other hand, the latter precipitation process has a disadvantage that the precipitated copolymer particles are ready to adhere to each other and agglomerate unless the polymer solution should be adjusted to a considerably low concentration and the poor solvent, such as water, should be used in large quantity.